The soupy, carbon dioxide-laden atmosphere that now swirls around Venus causes the temperature on the planet's surface to climb to lead-meltingly hot extremes.

The wispy atmosphere on Mars, while also heavy on the carbon dioxide, is no longer thick enough to preserve the water that researchers believe once flowed across the red planet's surface.

And while Saturn's moon Titan is also wrapped in a dense atmosphere, this one largely made up of nitrogen, temperatures are cold enough to cause methane rain to splash down on the moon's surface.

In some ways, the conditions on Venus, Mars and Titan couldn't be more different than those on Earth. But in other ways, the atmospheres on those celestial bodies may be among the best laboratories scientists on Earth have to understand our own climate and how it's changing.

Starting Monday, scientists will gather in Boulder for four days to discuss just that at the conference on Comparative Climatology of Terrestrial Planets, put on by the Lunar and Planetary Institute and focusing on Venus, Earth, Mars and Titan.

On Tuesday night, the conference is hosting a public panel discussion at the Boulder Theater called "Climate Change on Earth and Other Planets," featuring a keynote address by Bill Nye "The Science Guy."

Panelists include Jim Hansen, of NASA's Goddard Institute for Space Studies, who is well-known for his calls for urgent action to stem climate change on Earth; David Grinspoon, curator of astrobiology at the Denver Museum of Nature and Science; and Brian Toon, a researchers at the University of Colorado's Laboratory for Atmospheric and Space Physics.

"Earth is a very complex system," Grinspoon said. "The nearby planets -- especially the most earthlike -- are really priceless laboratories for us to test our ideas and our assumptions. When it comes to climate models in particular, we're banking a lot on getting it right."

While the climate on Earth is clearly different -- and much more hospitable to life as we know it -- than on the other atmosphere-wrapped, rocky planets in our solar system, the models used to understand our own climate should also work on those other planets once the inputs have been changed, given that the laws of physics still hold true. For example, carbon dioxide traps heat in any atmosphere and clouds reflect sunlight.

For example, the discovery that Venus was lacking oxygen compounds in its upper atmosphere and that Venus' upper atmosphere contained a little bit of chlorine helped researchers make the connection that chlorine compounds may deplete oxygen compounds in those locations. That bit of knowledge led scientists to then recognize that chlorine-containing compounds being released on Earth might be responsible for depleting the oxygen-rich ozone layer, according to Grinspoon.

Scientists are now looking to Venus to better understand global warming, since scientists believe that the planet's atmosphere once allowed for more moderate temperatures before a buildup of carbon dioxide caused a corresponding buildup of heat.

"Venus has the most extreme greenhouse climate in our solar system," Grinspoon said. "The history of Venus, as we understand it, is one of a runaway greenhouse. Basically, it's the same kind of dynamics and feedback as are going on in Earth's climate but gone completely awry."

CU's Toon said he'll be discussing a number of concepts during the event at the Boulder Theater that all relate to the creation of a planet's climate.

For example, some of the contributing factors include the planet's distance from the sun, its size, the amount of geologic activity, the cloud cover and, importantly, the thickness and makeup of the atmosphere. And those factors can interact in non-intuitive ways.

For example, Venus is closer to the sun than Earth, which means it receives more heat from the sun, but its atmosphere is extremely reflective, which could cool the planet. But because the atmosphere is saturated with carbon dioxide, the atmosphere absorbs and holds more heat.

And on Mars, the atmosphere also contains much more carbon dioxide than Earth's, but its distance from the sun helps counteract the atmosphere's warming effect.

"The basic summary is that there are common processes at work on all three of these planets and, probably, on other planets around other stars," said Toon, who works on a project that applies a climate model for Earth developed at the National Center for Atmospheric Research to Mars. "... By using the same models in different places, you convince yourself that the models are really working properly and that you understand the processes."

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